*{
    margin: 0;
    padding: 0;

}
body{
    background: #000;
}
a{
    text-decoration:none ;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%,-50%);
    font-size: 30px;
    /* 颜色外形 */
    background: linear-gradient(90deg,#039af4,#f23,#c4c4c4);
    background-size: 400%;
    width: 400px;
    height: 100px;
    color: aliceblue;
    line-height: 100px;
    text-align: center;
    border-radius: 50px;
}
a::before{
    content: "";
    position: absolute;
    left:-5px;
    right: -5px;
    bottom: -5px;
    top: -5px;
    background: linear-gradient(90deg,#039af4,#f23,#c4c4c4);
    background-size: 400%;
    border-radius: 50px;
    /* 虚化 */
    filter: blur(100px);
    /* 覆盖 */
     z-index:  1;
}
a:hover::before{
    animation: sun 8s infinite;
}
/* 悬停时产生效果 */
a:hover{
    animation: sun 8s infinite;
}
/* 动画颜色变换 */
@keyframes sun{
    100%{
        background-position: -400% 0;
    }
}